1. Field of the Invention
This invention generally relates to a multistage compression type rotary compressor, wherein a driving element and a first and a second rotary compression elements both driven by the driving element are arranged in a sealed container, and a refrigerant compressed by the first rotary compression element is discharged into the sealed container and the discharged intermediate pressure refrigerant is further compressed by the second rotary compression element. In addition, the present invention relates to a cooling device, in which a compressor, a gas cooler, a throttling means and an evaporator are connected in series.
2. Description of Related Art
Conventionally, in a multistage compression type rotary compressor, especially, in an internal intermediate pressure multiage (two stages) compression type rotary compressor, refrigerant gas is absorbed from an absorption port of the first rotary compression element arranged at the lower side to a low pressure chamber side of a lower cylinder. The refrigerant gas is thus compressed to possess an intermediate pressure due to an operation of roller and valve, and then discharged from a high pressure chamber side of an upper cylinder, through a discharging port and a discharging muffler chamber, and then into the sealed container. Thereafter, the intermediate pressure refrigerant gas in the sealed container is absorbed from an absorption port of the second rotary compression element arranged at the upper side into a low pressure chamber side in an upper cylinder. By an operation of roller and valve, the intermediate pressure refrigerant gas becomes high temperature and high pressure refrigerant gas. Then, the high temperature and high pressure refrigerant gas flows from the high pressure chamber side, through a discharging port and a discharging muffler chamber, and then to a radiator, at which a heat radiation is effectuated. After the heat radiation is effectuated, the refrigerant gas is throttled by an expansion valve and absorbs heat at the evaporator. Then, the refrigerant gas is absorbed into the first rotary compression element. The aforementioned refrigerant cycle is repeatedly conducted.
In the above rotary compressor, when refrigerant with a high difference between its high and low pressures is used, e.g., using carbon oxide (CO2) as refrigerant, the refrigerant pressure is 8 MPaG (intermediate pressure) at the first rotary compression element (as a lower side), and is a high pressure of 12 MPaG at the second rotary compression element (as a higher side).
As the carbon dioxide is compared with the conventional freon refrigerant, because of a high gas density, a sufficient freezing capability can be obtained even though the volume flow of the refrigerant is small. In other words, if the compressor possesses an ordinary ability, it is possible to reduce its displacement volume. But, in that case, since reduction in the inner diameter of the cylinder will cause a reduction of the compression efficiency, the thickness of the cylinder is made smaller and smaller.
However, as thinning the thickness of the cylinder, since refrigerant introduction pipes for introducing the refrigerant cannot be connected to the absorption side of each cylinder, and conventionally, the refrigerant introduction pipes are connected to an upper supporting member and a lower supporting member both of which are used to block an opening at the upper side of the upper cylinder and an opening at the lower side of the lower cylinder, as well as used as bearings of a rotational shaft. In this way, the refrigerant is introduced into each cylinder through each supporting member (referring to pages 7 and 8 of Japanese Laid Open Publication No. 2001-82369).
Furthermore, in a conventional cooling device, a rotary compressor (compressor), a gas cooler, a throttling means (an expansion valve, etc.) and an evaporator are sequentially and circularly connected in series with pipes so as to form a refrigerant cycle (a refrigerant circuit). The refrigerant gas is absorbed from an absorption port of a rotary compression element of the rotary compressor into a low pressure chamber side of a cylinder. By an operation of roller and valve, the refrigerant gas is compressed to form a high temperature and high pressure refrigerant gas. Then, the high temperature and high pressure refrigerant gas is discharged from a high pressure chamber side, through a discharging port and a discharging muffler chamber, and then to the gas cooler. After the refrigerant gas radiates heat at the gas cooler, the refrigerant gas is throttled by the throttling means, and then supplied to the evaporator where the refrigerant gas evaporates. At this time, the refrigerant gas absorbs heat from the ambient to effectuate a cooling effect.
In addition, for addressing the global environment issues in recent years, such cooling device does not use the Freon type refrigerant, and a cooling device for the refrigerant cycle, in which a nature refrigerant (e.g., carbon oxide, CO2) is used as the refrigerant, is developed.
In such a cooling device, in order to prevent the liquid refrigerant from returning back to the compressor to cause a liquid compression, an accumulator is arranged between an outlet side of the evaporator and an absorption side of the compressor. The cooling device is thus constructed in a structure where the liquid refrigerant is accumulated in the accumulator and only the gas refrigerant is absorbed into the compressor. The throttling means is adjusted in a manner so that the liquid refrigerant in the accumulator does not return back to the compressor (referring to Japanese Publication No. H07-18602).
However, in a case that the compressor has a larger capability than above, a cylinder with a thick dimension can also be used to connect the refrigerant pipes. Therefore, different from the above case, the refrigerant introduction pipes can be connected to the upper and lower cylinders that form the first and the second rotary compression elements without passing through the supporting members. In that case, however, since the distance between the upper and lower refrigerant introduction pipes is too close, it will cause a problem that a pressure resistance strength (8 MPaG) of the sealed container between the pipe connection portions cannot be maintained.
On the other hand, regarding the installation of the accumulator at the low pressure side of the refrigerant cycle, a refrigerant filling amount is required to be large. In addition, for preventing a liquid back flow phenomenon, the aperture of the throttling means is reduced, or the capacity of the accumulator has to be increased, which will cause a reduction of the cooling ability or an enlargement of the installation space.
In addition, since the compression ratio is very high and the temperature of the compressor itself and/or the temperature of the refrigerant gas discharged to the refrigerant cycle are high, it is very difficult that the evaporation temperature at the evaporator is below 0° C., for example, at an extreme low temperature range below 50° C.